Cotton harvesters typically include two or more cotton harvesting units arranged at a forward end of a frame for removing cotton from rows of cotton plants. Each harvesting unit has a pair of picker drums including vertically spaced rows of rotary picker spindles for removing the cotton from the plants.
A cotton-conveying system transports the harvested cotton from the harvesting unit to a receptacle mounted on the frame of the cotton harvester. The conveying system includes walled ducts extending upwardly from the harvesting units toward the receptacle and air jets for drawing the harvested cotton from the harvesting units and propelling the cotton through the ducts.
For one reason or another, the harvested cotton may clog the duct through which it travels en route to the receptacle and stop the flow of cotton from the cotton plants to the receptacle. Should a blockage or clog result, the operator would not know of the blockage until he observes that no cotton is passing through the outlet of the duct. This may be difficult to detect, as many large automatic cotton pickers are provided with several ducts through which the cotton flows en route to the receptacle. Therefore, should one of the ducts become blocked or clogged, it may be difficult to detect since cotton is still coming out of the other ducts.
Various types of monitoring systems have been devised to detect blockages in cotton harvesters which have air conveying systems for moving harvested cotton from the harvesting units to the cotton receptacle. One type of monitoring system includes a photoelectric detector which is responsive to cotton flow through the duct. Photoelectric detectors, however, are susceptible to dirt, grease, water and plant saps carried by the harvested cotton conveyed therepast and which clouds the face of the detector.
Thermistors and thermocouple sensors are known for monitoring airflow in a duct. The thermistor or thermocouple-type sensors are sensitive and require relative complex circuitry which must be carefully calibrated to achieve accurate results. Monitoring systems which use pressure-responsive monitors or sensors are also expensive and are also difficult to calibrate.